1. Field of the Invention
This invention relates to a method of producing a high-quality amorphous alloy thin strip as a new industrial product and at low production cost. The strip is highly useful for commercial frequency band transformers which typically have operating frequencies of 50Hz and 60Hz.
2. Description of the Related Art
Japanese Patent Application Laid-Open No. 57-116750 (Patent Family, EP55327, CA1215235) discloses an alloy for use in the production of amorphous alloy thin strip for commercial frequency band transformers. The alloy disclosed is at least 90% amorphous and has a composition which can be substantially expressed by the formula Fe.sub.a Si.sub.b B.sub.c, where ".sub.a ", ".sub.b " and ".sub.c " respectively represent approximately 75 to 78.5 atomic %, approximately 4 to 10.5 atomic %, and approximately 11 to 21 atomic %, the sum of ".sub.a ", ".sub.b " and ".sub.c " being 100.
Conventionally, amorphous alloys for commercial frequency band transformers have been produced in the manner as shown in FIG. 6 of the drawings, where the materials are fed into a melting furnace 17 and, after adjustment of composition and temperature, are formed into a thin strip by quenching. The materials used in the process are agglomerated after smelting and then melted again. Referring to FIG. 6, numeral 11 indicates a tundish; numeral 12 a cooling roll; and numeral 15 a device for taking up the strip 14.
The electric melting furnace system in which the materials are melted again presents various problems. For example, it requires use of high-purity ferroboron, which is rather expensive. Further, the system requires a high-quality iron source since the process it performs is incapable of eliminating impurities. In addition, it involves energy loss, reduction in material yield, difficulty in achieving mass production due to the melting in small amounts and other problems.
Thus, there has been no optimum process available for effective mass production of an amorphous alloy for use in commercial frequency band transformers.
In the field of steel production, an electromagnetic silicon steel plate production technique has also been established. For example, high-quality molten steel may be obtained through a series of processes using, as shown in FIG. 7 of the drawings, a blast furnace 1, hot metal pre-processing apparatuses 2 and 4, a converter 5, and, as needed, a vacuum degasifying apparatus.
This molten steel, intended for the production of electromagnetic silicon steel plates differs significantly, however, from amorphous alloy thin strip useful in commercial frequency band transformers, with important differences of boron and silicon contents.
If the composition of the electromagnetic silicon steel of the prior art were adjusted to the formula of the amorphous alloy by the process of the prior art, boron contamination would occur, resulting in other process materials being contaminated. Further, it should be noted that the melting of the prior art molten steel for the production of electromagnetic silicon steel plates is effected in the order of several hundreds of tons, which is too large for the production of an amorphous alloy in terms of heat size.
Thus, in actual practice, the prior art process cannot be employed for the effective commercial production of a high-quality amorphous alloy thin strip.